Don't fail on tests if Test::Difference is not installed.

  Closes #3
  Thanks Sander Lepik for reporting.
v1.001002

 [Bugfix]
 - Don't fail on tests if Test::Difference is not installed.
 - Closes #3
 - Thanks Sander Lepik for reporting.

 [Dependencies::Stats]
 - Dependencies changed since 1.001001, see misc/*.deps* for details
 - develop: (suggests: ↑1)
post-release cleanup